Hydraulic actuators in the past have been made insensitive to tubing pressure using opposed pistons that create opposing forces to any tubing pressure so that the net result is no movement of the actuator mechanism so that the tool is not set even if there are pressure surges in the tubing. To insure that there is no premature setting the sleeve to be moved to set the tool can be held with a shear pin that breaks under a predetermined net force. Tool actuation involves isolating an upper inlet to one of the pistons from a lower inlet to an opposing piston, such as with an object dropped on a seat in the tubing. This is followed with elevating the pressure to one of the pistons that has access to tubing pressure above the seated object so that one piston creates a net force in the setting direction for setting the tool. A retainer for the setting sleeve can be broken in the setting process as the tool is set with the actuator. This design is shown in schematic terms in U.S. Pat. No. 7,766,088. While this reference mentions in passing an application for unsetting a tool, the details provided focus on how to set and no details are provided as to how to unset with the described actuation tool.
U.S. Pat. No. 7,686,090 shows the use of a floating piston in a liner hanger actuation tool with a balance piston referenced to the annulus. US Publication 2010/0319927 shows the use of a ball seat that can be displaced with a seated ball on it into a larger diameter for release of the ball.
The present invention goes a step further by initial isolation of one actuating piston to set a tool such as a liner hanger and then isolation of an opposing piston to tubing pressure to reverse the movement of an actuation mechanism for release of the tool such as a liner hanger. Those skilled in the art will more readily appreciate various aspects of the invention from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.